by constraints on consumption (e.g., housing) that have contributed to postponement of marriage and childbearing.* As of 1960 on the natality side the demographic transition had progressed substantially in almost all countries of European background, whether Catholic or non-Catholic, communist or non-communist, and it has advanced even further today. Now the dichotomy in natality is beginning to break down. With major socioeconomic changes, an increasing number of less developed countries are experiencing reductions in fertility. These changes since the postwar period give promise of a new continuum of countries at various stages moving from high to low birth rates. THE PENETRATION OF FORMER BARRIERS TO NATALITY REDUCTION The scope of the changes that are occurring is evidenced by widespread reduction of birth rates in the 1960's and especially by the growing number of less developed countries in natality transition. The average less developed country today has a birth rate of 40 or so, more often higher than lower. Some forty-seven less developed countries are listed by the United Nations as having "virtually complete" vital statistics, i.e., at least 90 percent coverage of births. Of these, forty-two report a reduction of the birth rate between the average for 1960-64 and the available data for the second half of the decade.t Many of the "countries" listed by the United Nations are small areas. The birth rates for countries of 500,000 or more inhabitants are shown in Table 1. Various stages in natality transition are clearly observable. In some countries reduction of the birth rate began in the 1950's and continued through the 1960's. In others it was initiated in the 1960's. In several (e.g., Guatemala, Mexico, and Panama) it is too early to state whether or not the drop in the birth rate is the first stage in continuous transition or merely the result of changes in age structure or of vagaries in statistical reporting.$ *Communist experience, and especially the important role of providing free abortion, has not been given the attention it deserves in the family planning programs of the less developed countries. See Abdel R. Omran, "Abortion in the Demographic Transition," in this volume. tine exceptions are Israel (actually a developed country in an underdeveloped region), Jordan, and three very small areas (Nauru, Norfolk Island, and the U.S. Virgin Islands). $Among the influences at work are the following examples: the improvement (less often deterioration) in the completeness of birth registration, which would usually raise recent figures relative to earlier ones; the provisional nature of most recent rates (final figures are often, though not always, somewhat higher than the provisional); changes in age structure, i.e., in the proportion of children and of persons in reproductive ages in the total population; errors in estimates of population used as the denominator in computation of birth rates. The often contradictory effects of these influences will be clarified bv the results of 1970 and 1971 censuses where these are beinc taken.